The method of using a venturi to increase the velocity of a water flow is old. The embodiment has the following aspects which the inventor believes are new.
1) The front shroud is flexible (collapsible) on demand.
2) The front shroud can be pursed (drawn) together to stop water from flowing through it and the turbine.
3) The purse line can be released to allow water to flow through the front shroud and turbine.
4) A combination of a flexible front and a rigid rear shroud used together as one unit.
5) The method of pursing a flexible shroud to stop the rotation of a turbine.
6) The method of using a flotation chamber to raise a turbine to the surface to be serviced.
One of the problems inherent in a low head (run of the river, tidal, etc.) turbine for producing electricity is the relatively slow water velocity; usually from 1 to 5 knots. This device that incorporates two shrouds (one front, one rear) increases the water velocity flowing through the turbine.
This ability to increase low head water velocities to those of high head applications has inherent advantages of cost, size, efficiency and overall maintainability. Since horsepower output is on an exponential curve with water velocity, it is expedient to keep the blade diameter as small as possible to reach the goal power output. This embodiment does that by the use of shrouds. Overall cost per kilowatt hour is lower when shrouds are used since the shrouds are the least expensive component of the machine.
The collapsible front shroud, when pursed, provides a rapid means of shutting down the turbine.